Modern-day escalators and moving walkway passenger conveyors are equipped with moving handrails which must be moved in synchronization with the conveyor treads upon which the passengers stand. The passenger treads are typically interconnected by step chains which are mounted about step chain sprockets. The step chain sprockets include a set of drive sprockets at one end of the conveyor and a pair of return sprockets at the opposite end of the conveyor. The step chain drive sprockets are connected to an electric drive motor by means of a drive chain. Thus, there are a plurality of chains that are employed to provide tread movement to the conveyor.
The handrail will typically be driven by means of a friction roll, or by a friction belt, which engages the handrail directly. The handrail drive will derive its motive power from the tread drive train, or directly from the main drive. Since the tread drive chain and the main drive both involve the use of several chains, passengers will be able to detect pulsations in the handrail's movement due to the chordal condition of the chains as they pass over the chain return sprockets. This problem has been recognized in the prior art, and a number of different solutions thereto have been suggested. U.S. Pat. Nos. 2,491,974 granted Dec. 20, 1949 and 3,499,340 granted Mar. 10, 1970, both describe a drive for a moving stairway wherein the drive sprocket includes elastomeric chain-engaging inserts on the sprocket for damping vibrations between the sprocket and chain during operation of the escalator. U.S. Pat. No. 3,658,166 granted Apr. 25, 1972 describes the use of an intermediate drive sprocket on a step chain, which intermediate sprocket engages the step chain at a location in between the chain reversal sprockets, and which intermediate sprocket is provided with involute teeth that mesh with the chain and are operable to smooth out movement of the step chain. Other efforts to smooth step chain movement have involved the use of enlarged diameter drive sprockets which, due to their enlarged diameters, reduce the size of each chordal step on the sprocket, and thus reduces the magnitude of chordal jerks imparted to the step chain by the drive sprocket.
Soviet Inventor's Certificate No. SU 1,530,558A1, published Dec. 23, 1989, describes an escalator handrail drive assembly which derives its motive power from the main escalator step chain drive. The handrail drive sprocket is connected to the step chain drive sprocket by means of a plurality of bolts which extend through shock absorbing elastomeric bushings so as to reduce the noise level of the escalator.
Recapping the aforesaid solutions to escalator chordally-induced jerks imparted to the handrail drive and the handrail, the use of damping inserts in the chain sprockets does not prevent sprocket teeth from jerking the chains. The use of enlarged drive sprockets has its limits due to available installation envelopes for the escalator drive mechanisms. The use of auxiliary drive sprockets in the step chain drive chain is expensive and space-consuming. Finally, the use of bolts and elastomeric bushings provides a degree of vibration damping, but the use of bolts provides a limiting factor which restricts the degree of damping for the handrail.
It would be highly desirable to provide a step chain drive to handrail drive connection which can completely damp out step chain jerks from being transmitted to the handrail drive so that handrail movement will be smooth and devoid of jerkiness.